Mixing Versus Sorting in Schooling: Evidence from the Equalization Policy in South Koea

This paper examines the effects of sorting and mixing on academic performance of high school students in South Korea. The Korean government has vigorously promoted mixing for more than three decades, replacing competitive entrance examinations at individual schools by a lottery-based enrollment system. As a result, about half of high schools (grades 10 to 12) as well as all middle schools (grades 7 to 9) are subject to what is locally known as the Equalization Policy (EP), and passively accept students randomly assigned. In contrast, outside the designated EP areas, students are sorted with stratification along ability among schools. This paper employs the difference-in-differences empirical strategy to analyze the newly available data from the Korean National Assessment of Educational Achievement. Two main results emerge. First, sorting raises test scores of students outside the EP areas by roughly 0.3 standard deviations, relative to mixing. Second, more surprisingly, quantile regression results reveal that sorting benefits students across the ability distribution